1. Field of the Invention
The present invention relates to an apparatus and a method for detecting a signal with a low complexity and a performance similar to Maximum Likelihood (ML) detection, by reducing a search space in a Multiple-Input Multiple-Output (MIMO) system.
2. Description of the Related Art
In a multi-antenna system utilizing Multiple-Input Multiple-Output (MIMO), an optical detection scheme for receiving a plurality of independent symbols via the multiple antennas is a Maximum Likelihood (ML) detection in terms of a symbol error rate.
Disadvantageously, however, the high complexity of the ML detection method complicates its implementation. Therefore, various linear detection schemes, for example, detection schemes using Zero Forcing (ZF) or Minimum Mean Square Error (MMSE) have been utilized, and a nonlinear Vertical-Bell Labs layered Space Time (V-BLAST) has been used as well.
Still, these schemes do not always provide satisfactory performance. In this regard, schemes demonstrating the performance similar to the ML scheme with a little more complexity have been suggested.
For example, a QR decomposition with M-algorithm (QRM-MLD) and a Sphere Decoding (SD) scheme execute a tree search algorithm using QR decomposition. Q denotes an orthogonal matrix and R denotes an upper triangular matrix.
The QRM-MLD scheme exhibits a lower complexity than the ML scheme but still has a large number of symbol candidates to consider. The SD scheme suffers the considerable change of the complexity according to a radius of a hyper-sphere.